This longitudinal study is an examination of the relationship between marijuana use and the assumption of adult roles, as well as the relationship between assuming adult roles and the likelihood of later marijuana use. Data were collected at 5 points in time from childhood through early adulthood (late 20s) by means of a structured questionnaire. Participants’ marijuana use and the assumption of adult roles, including employment, marriage, parenthood, and living arrangements, were measured, and the data were analyzed with logistic regression analyses. A history of marijuana use was associated with an increased risk of adopting more unconventional adult roles, such as postponement of marriage, having a child out of wedlock, and unemployment. These results suggest that frequent prior marijuana use may adversely affect one’s ability to successfully assume conventional adult roles. Furthermore, controlling for earlier marijuana use, marriage during early adulthood significantly decreased the risk of later marijuana use.

THE PERIOD BETWEEN ADOLESCENCE and the late 20s is a critical transitional period during which the young adult is expected to assume new life roles, such as joining the work force, marrying, and becoming a parent. According to Jersild, Brook, and Brook (1978), some youngsters make this transition with relative ease, whereas others have considerable difficulty in assuming adult roles. Aseltine and Gore (1993) pointed out that a number of dysfunctional adolescents are able to assume adult responsibilities; at the same time, there are a number of well-adjusted adolescents who find it extremely difficult to assume adult responsibilities. Such difficulty has negative consequences for the individual and society (Elder, 1978). Therefore, identifying the factors during adolescence that promote or allow a successful transition into adulthood has important implications for both prevention and treatment of dysfunctional development.

In the present study, we focused on frequent marijuana use, a problem behavior common during adolescence and young adulthood that may have important implications for an individual’s present and future functioning. Our main goal was to examine the consequences of marijuana use for future adult functioning; of particular interest was the extent to which marijuana use is a risk factor for the postponement of normative adult roles or the assumption of more unconventional adult roles. A secondary goal of this study was to explore the relationship between the assumption or postponement of adult roles and later marijuana use.

We examined three components of the “gateway theory” in relation to marijuana use: (1) whether adolescent marijuana use predicts young adult drug use, (2) whether this association persists when controlling for similar family background, (3) whether common genetic or environmental factors contribute to the association. The three components were tested in adolescents from the National Longitudinal Study of Adolescent Health assessed twice during adolescence and then re-interviewed 5 years later. Component 1 was tested in 18,286 subjects, component 2 in sibling pairs ( n=360) discordant for marijuana use, and component 3 in a genetically informative sub-sample ( n=4846). Marijuana use was defined as any use during adolescence, and drug use was defined as self-reported past year use of other illicit drugs besides marijuana. Marijuana users were twice as likely to use illicit drugs as young adults than non-users. Shared environmental factors mediated much of the relationship between adolescent marijuana use and young adult drug use. The association remained, however, even when controlling for familial environmental and other measured factors.

Background While it has been demonstrated that smoking cigarettes in adolescence increases the likelihood of progressing to marijuana use, few studies have considered the reverse scenario in which early use of cannabis leads to greater tobacco smoking.

Methods Participants (n=5963), who had never smoked cigarettes daily by wave I of the National Longitudinal Study of Adolescent Health, were followed 6 years (waves I–III) from adolescence into young adulthood. Measures of marijuana use (lifetime use, monthly use, age at first use), as assessed at wave I within 12–16 (n=3712) and 17–21 (n=2251) year-olds, were separately modeled as predictors of three tobacco-related outcomes: (1) age at onset of daily cigarette smoking, (2) lifetime nicotine dependence, (3) current nicotine dependence.

Results In the older cohort (17–21-year-olds at wave I), lifetime (>10 times) and past-month marijuana use at wave I were predictive of an earlier initiation into daily cigarette smoking and a greater likelihood of developing nicotine dependence by wave III. Furthermore, age at first use of cannabis was negatively associated with risk of nicotine dependence in the older, but not younger cohort.

Conclusion After controlling for baseline measures of tobacco smoking and other demographic risk factors, the use of marijuana in adolescence was modestly associated with daily cigarette smoking and nicotine dependence in young adulthood.

4. Age of alcohol and marijuana use onset predicts weekly substance use (2010)

The present study examined whether age of alcohol and marijuana use onset during adolescence predicted later substance use and related problems in several areas of psychosocial functioning among young adults. A total of 621 participants completed surveys regarding current substance use from 7th through 12th grades and also completed a survey as young adults (age 24) that included questions regarding the impact of alcohol and drug use on several areas of functioning. Findings indicated that earlier age of substance use onset was positively associated with weekly use of alcohol and marijuana during young adulthood, as well as substance-related occupational, relationship, and legal problems. The majority of young adults reporting problems due to alcohol or drug use had first reported alcohol and/or marijuana use before entering high school. For women, onset of substance use prior to high school was more strongly related to negative drug-related occupational outcomes than was concurrent weekly substance use as a young adult. Findings indicated that the negative effects of early onset substance use are strongest in social and occupational functioning, areas that correspond to the DSM criteria relevant to the diagnosis of alcohol or substance use disorder.

Aims: Alcohol and marijuana are the most widely used intoxicants among adolescents, yet their potential unique and interactive influences on the developing brain are not well established. Brain regions subserving learning and memory undergo continued maturation during adolescence, and may be particularly susceptible to substance-related neurotoxic damage. In this study, we characterize brain response during verbal learning among adolescent users of alcohol and marijuana.

Findings: Groups demonstrated no differences in performance on the verbal encoding task, yet exhibited different brain response patterns. A main effect of drinking pointed to decreased inferior frontal but increased dorsal frontal and parietal fMRI response among binge drinkers. There was no main effect of marijuana use. Binge drinking x marijuana interactions were found in bilateral frontal regions, where users of either alcohol or marijuana showed greater response than non-users, but users of both substances resembled non-users.

Conclusions: Adolescent substance users demonstrated altered fMRI response relative to non-using controls, yet binge drinking appeared to be associated with more differences in activation than marijuana use. Alcohol and marijuana may have interactive effects that alter these differences, particularly in prefrontal brain regions.

6. The Impacts of Adolescent Alcohol and Marijuana Use Onset on Cognition (2013)

THE ADOLESCENT BRAIN has a lot of developing to do as it transforms the child’s brain to that of an adult. Some researchers are worried about how marijuana use might affect that process. A growing number of studies report that regular use of marijuana, (Cannabis sativa), changes the structure of the adolescent brain, specifically those areas that are involved with memory and problem solving (Lisdahl et al., 2013; Smith et al., 2014). These may, in turn, affect cognition and academic performance. According to a recent report regular marijuana users, defined as more than once a week, have, on average, a school grade point one grade point lower than matched peers that do not smoke marijuana (Lisdahl et al., 2013). A second study analyzed compared IQ scores in childhood through age 38 among marijuana users and nonusers (Meier et al., 2012). It found that people using marijuana in their teenage years and then continuing to use marijuana for many years lost about eight IQ points from childhood to adulthood, whereas those who never used marijuana did not lose any points.

Jacobus, Joanna, VA San Diego Healthcare System, La Jolla, CA, US
Squeglia, Lindsay M., Department of Psychiatry, University of California San Diego, San Diego, CA, US
Infante, M. Alejandra, San Diego State University, San Diego, CA, US
et al.

Neuropsychology, Vol 29(6), Nov, 2015. pp. 829-843.

Objective: The effect of adolescent marijuana use on brain development remains unclear despite relaxing legal restrictions, decreased perceived harm, and increasing use rates among youth. The aim of this 3-year prospective study was to evaluate the long-term neurocognitive effects of adolescent marijuana use. Method: Adolescent marijuana users with concomitant alcohol use and control teens with limited substance use histories were given neuropsychological and substance use assessments at project baseline, when they were ages 16–19. They were then reassessed 18 and 36 months later. Changes in neuropsychological measures were evaluated with repeated measures analysis of covariance, controlling for lifetime alcohol use, and examined the effects of group, time, and group by time interactions on cognitive functioning. Results: MJ + ALC users performed significantly worse than controls, across time points, in the domains of complex attention, memory, processing speed, and visuospatial functioning. Earlier age of marijuana use onset was associated with poorer processing speed and executive functioning by the 3-year follow-up. Conclusions: Frequent marijuana use throughout adolescence and into young adulthood appeared linked to worsened cognitive performance. Earlier age of onset appears to be associated with poorer neurocognitive outcomes that emerge by young adulthood, providing further support for the notion that the brain may be uniquely sensitive to frequent marijuana exposure during the adolescent phase of neurodevelopment. Continued follow-up of adolescent marijuana users will determine the extent of neural recovery that may occur if use abates.

• Adolescent marijuana and alcohol users show thicker cortices compared to controls.
• More cumulative marijuana use is associated with increased cortical thickness.
• More cumulative alcohol use is associated with decreased cortical thickness.
• Regular marijuana and alcohol use may have a deleterious impact on adolescent brain development.

Studies suggest marijuana impacts gray and white matter neural tissue development, however few prospective studies have determined the relationship between cortical thickness and cannabis use spanning adolescence to young adulthood. This study aimed to understand how heavy marijuana use influences cortical thickness trajectories across adolescence. Subjects were adolescents with heavy marijuana use and concomitant alcohol use and controls with limited substance use histories. Participants underwent magnetic resonance imaging and comprehensive substance use assessment at three independent time points. Repeated measures analysis of covariance was used to look at main effects of group, time, and Group×Time interactions on cortical thickness. MJ+ALC showed thicker cortical estimates across the brain (23 regions), particularly in frontal and parietal lobes. More cumulative marijuana use was associated with increased thickness estimates by 3-year follow-up. Heavy marijuana use during adolescence and into young adulthood may be associated with altered neural tissue development and interference with neuromaturation that can have neurobehavioral consequences. Continued follow-up of adolescent marijuana users will help understand ongoing neural changes that are associated with development of problematic use into adulthood, as well as potential for neural recovery with cessation of use.

Introduction Orbitofrontal (OFC) circuits have been implicated in the pathophysiology of substance use disorders. The current study examined OFC functional connectivity differences in marijuana-using adolescents (MJ) and non-using healthy controls (HC).

Methods Functional magnetic resonance imaging (fMRI) resting-state data were obtained on a 3T MRI scanner on 31 HC and 43 heavy MJ smokers. Image analyses were performed between groups (MJ, HC) for the left and right OFC separately. Regression analyses between OFC functional connectivity and lifetime MJ use, age of first MJ use and impulsivity also were performed.

Results Increased OFC functional connectivity to frontal and motor regions was observed in heavy MJ users compared to HC. Earlier age of first MJ use was associated with increased functional connectivity of the right OFC to motor regions. High lifetime MJ use was associated with increased OFC functional connectivity to posterior brain regions in MJ youth.

Discussion Findings indicate atypical OFC functional connectivity patterns in attentional/executive, motor and reward networks in adolescents with heavy MJ use. These anomalies may be related to suboptimal decision making capacities and increased impulsivity. Results also suggest different OFC connectivity patterns may be present in adolescents with early onset of MJ use and high lifetime exposure to MJ.

• Early onset MJ use was associated with different patterns of cortical architecture.
• Early vs. late onset divergence was in brain regions underlying higher-order cognition.
• Findings were above and beyond effects of alcohol and current age.

Background As the most commonly used illicit substance during early adolescence, long-term or latent effects of early adolescent marijuana use across adolescent developmental processes remain to be determined.

Methods We examined cortical thickness, gray/white matter border contrast (GWR) and local gyrification index (LGI) in 42 marijuana (MJ) users. Voxelwise regressions assessed early-onset (age 16 and below) vs. late-onset (older than 16 years-old) differences and relationships to continued use while controlling for current age and alcohol use.

Results Although groups did not differ by onset status, groups diverged in their correlations between cannabis use and cortical architecture. Among early-onset users, continued years of MJ use and current MJ consumption were associated with thicker cortex, increased GWR and decreased LGI. Late-onset users exhibited the opposite pattern. This divergence was observed in all three morphological measures in the anterior dorsolateral frontal cortex.

Conclusions Divergent patterns between current MJ use and elements of cortical architecture were associated with early MJ use onset. Considering brain development in early adolescence, findings are consistent with disruptions in pruning. However, divergence with continued use for many years thereafter suggests altered trajectories of brain maturation during late adolescence and beyond.

• Adolescent marijuana use and emotional functioning across time points were examined.
• Resiliency increased in controls but not heavy marijuana users across time points.
• Negative emotionality decreased in controls but not heavy marijuana users across time points.
• Heavy marijuana users had blunted brain activity to negative words relative to controls.
• Brain activity mediated the effect of marijuana use on later emotional functioning.

This work investigated the impact of heavy marijuana use during adolescence on emotional functioning, as well as the brain functional mediators of this effect. Participants were recruited from the Michigan Longitudinal Study (MLS). Data on marijuana use were collected prospectively beginning in childhood as part of the MLS. Participants were classified as heavy marijuana users or controls with minimal marijuana use. Two facets of emotional functioning—negative emotionality and resiliency (a self-regulatory mechanism)—were assessed as part of the MLS at three time points: mean age 13.4, mean age 19.6, and mean age 23.1. Functional neuroimaging data during an emotion-arousal word task were collected at mean age 20.2. Negative emotionality decreased and resiliency increased across the three time points in controls but not heavy marijuana users. Compared with controls, heavy marijuana users had less activation to negative words in temporal, prefrontal, and occipital cortices, insula, and amygdala. Activation of dorsolateral prefrontal cortex to negative words mediated an association between marijuana group and later negative emotionality. Activation of the cuneus/lingual gyrus mediated an association between marijuana group and later resiliency. Results support growing evidence that heavy marijuana use during adolescence affects later emotional outcomes.